# Calculating least sterilization z value

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### #1 Paul keida

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Posted 16 September 2016 - 02:52 PM

i need help determining z values with a temperature change

i have a client who mfg a salad dressing with a ph of 3.0 and CCP is less than 3.5

he heats with the current process to 200F and holds for 5 minutes , cools and hot fills at 180F and inverts for 2 minutes

how would Z values compare if he reduces heat to 195F and holds for 1 minute , then hot fills at 180F

is there software to compare heat treatments to themal death rate to maintain 5 log reduction ?

thx

### #2 Charles.C

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Posted 17 September 2016 - 02:53 AM

i need help determining z values with a temperature change

i have a client who mfg a salad dressing with a ph of 3.0 and CCP is less than 3.5

he heats with the current process to 200F and holds for 5 minutes , cools and hot fills at 180F and inverts for 2 minutes

how would Z values compare if he reduces heat to 195F and holds for 1 minute , then hot fills at 180F

is there software to compare heat treatments to themal death rate to maintain 5 log reduction ?

thx

Hi Paul,

Not really my area but I deduce from IT that -

"salad dressing" may be FDA regarded as an acid food rather than an acidified one.

The crude  F(T,z) lethality values for each stage (assumed to refer constant, coldest temp. point ) can be calculated as per analogous formula to that in this attachment -

Strictly you will need appropriate z-value.

The "121"/z values should, i think, preferably be referenced to a level close to yr pasteurizing temperature (eg.90degC). Maybe can try z= 10 for both temps in degC just to get an idea. Then add the 2 stages together.

Conservatively, could calculate for 1st stage only, eg ca. (5).[10 ^((93.3-90)/10)] = 10.7 for 1st option. Similarly > 1.12 for 2nd option.

And yes, excel programs for F are available and posted on this forum (somewhere). Particularly developed for temperatures not constant.

The above calculation compares yr applied F values.

Afaik the Z value itself  is based on the applied lethality achieving a typical 5log bacterial reduction of species XYZ so may/may not be satisfied by the F values above.

This "validation" step requires a further calculation to determine No.of log reductions of XYZ achieved.

(In practice, i believe  Z- "least sterilization values" may have additional safety factors built in also).

So the final step probably requires your specifying a relevant XYZ species, eg L.monocytogenes, determining (searching for) its appropriate D (Decimal Reduction) value for the food matrix involved, and applying one more calculation.

PS - this ref. contains  recommended heat processing time/temperature combinations for a 5-log reduction in bacterial pathogens for acidified products with a pH of 4.1 or below -

An additional table was issued in a Draft FDA document (2010) -

Kind Regards,

Charles.C

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### #3 Charles.C

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Posted 26 September 2016 - 12:42 PM

Hi Paul,

I noticed later that yr actual thread title was seeking "least sterilizing value" (LSV). This might have additional  expectations as compared to my interpretation of the queries in OP as seeking a lethality value based on a specific pathogen.

As I understand, LSV (as related to filing forms for "scheduled processes")  can have a rather complicated interpretation and typically seems to be usually reserved for a Process Authority's enumeration. For example see this 2015 thread -

http://www.ifsqn.com...water-activity/

I have since seen some further indication that the LSV value does relate to an assessment including both terms (a,b) within the practical context of ensuring "commercial sterility" however i have been unable  to determine whether a particular microbial species is routinely used for the additional "b" requirement or if it varies depending on the product. The latter seems more logical.

PS - further info. -

the F0 (lowest sterilizing value) of the process which results in a commercially sterile product. An F0 of 3.0 minutes is required to achieve a 12 log reduction of Clostridium botulinum1. A higher F0 is required to prevent the growth of non-pathogenic thermophilic spoilage organisms. The F0 is the single value of the lowest sterilizing value achieved by the process.

1It is internationally accepted that a minimum sterilizing value of 3.0 minutes is required to render a low-acid canned food microbiologically safe (Huss H. H et al., 2003)

[ref. Huss, H.H; Ababouch, L; Gram, L. (2003) Assessment and Management of Seafood Safety and Quality. Clostridium botulinum Fisheries Technical Paper. No. 444. Rome, Clostridium botulinum]

Kind Regards,

Charles.C

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